FileZilla uses whatever the default action for that file type is. Looks like Libre Office claimed the association to the file type, you simply need to change it back.

### BEGIN SIGNATURE BLOCK ###No support requests per PM! You will NOT get any reply!!!
FTP connection problems? Do yourself a favor and read Network Configuration.All FileZilla products fully support IPv6.http://worldipv6launch.org
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### BEGIN SIGNATURE BLOCK ###No support requests per PM! You will NOT get any reply!!!
FTP connection problems? Do yourself a favor and read Network Configuration.All FileZilla products fully support IPv6.http://worldipv6launch.org
### END SIGNATURE BLOCK ###